Compound transmission systems comprising manually shifted multispeed main transmission sections connected in series with one or more multispeed auxiliary transmission sections, usually of the range, splitter, or combined range/splitter type are widely utilized in heavy duty vehicles. Examples of such compound systems may be seen by reference to U.S. Pat. Nos. 3,283,613 and 4,754,665; the disclosures of which are herein incorporated by reference. By utilizing main and auxiliary transmission sections connected in series, assuming proper sizing of the ratio steps, the total of available transmission ratios is equal to the product of the main and auxiliary section ratios.
For heavy equipment, such as trucks and tractors, traditional compound transmission systems have always compromised between addressing the operating needs of first and second owners. Typically, the first owner desires a low cost of operation with particular emphasis on fuel economy. As a result, the first owner would prefer a transmission with fewer speeds to always compromised between addressing the operating needs of first and second owners. Typically, the first owner desires a low cost of operation with particular emphasis on fuel economy. As a result, the first owner would prefer a transmission with fewer speeds to minimize skill level, a direct drive top gear to minimize power losses, and a geared cruise speed of 55-58 mph to minimize aerodynamic losses. This strategy is in conflict with a typical second owner, who places more value on performance than economy. The second owner would prefer a short step, overdrive transmission with a geared cruise speed of 65 mph. This conflict culminates in depressed resale values between the first and second owners.
In an attempt to provide a transmission which may be configured for both first and second owners, lockout devices have been utilized to prevent operation of the transmission by the first owner in a given combination of gear ratios. Upon resale, the lockout device is removed, thereby providing a full set of gear ratios for the second owner. Such lockout devices are normally enclosed within the transmission housing and cannot be removed or rendered inoperable without disassembling the entire transmission. U.S. Pat. No. 5,284,065 to Loeffler et al. discloses a lockout device which precludes the use of a single, overdrive top gear in the first owner configuration, and may be removed without transmission disassembly to provide the overdrive gear in the second owner configuration. While this device represents one solution, the availability of multiple, additional overdrive speeds in the second owner configuration would add further to the resale value of the vehicle between first and second owners.
Therefore, a need exists for a compound transmission which provides one set of gear ratios for the first owner of a vehicle, and may be converted to provide a plurality of additional gear ratios for the second owner of the vehicle without requiring disassembly and reassembly of significant portions of the transmission.